This invention relates to the field of disaster recovery systems. In particular, the presently disclosed inventive concepts relates to a copy-on-read process in a disaster recovery system.
When a storage system replicates volumes to disaster recovery (DR) locations, the initial replication can take some time. There is often a requirement to mount the volumes at the DR location on a server system, which may only happen once the initial replication has completed. This means that the total time that passes before having the volumes successfully mounted is greater than it need be.
In the prior art, an initial synchronisation process may typically be driven from the production or primary system, using a high water mark or bitmap to drive copying each region in turn. The primary system will read a region from the primary storage, and transmit it to the DR system, which will write it to the DR storage. Before a region has been copied to the secondary system, host writes to that region are allowed to update the primary storage without needing to immediately replicate that change to the DR system. After a region has been copied, the primary system ensures that subsequent host writes to that region are immediately replicated to the DR storage in order to keep the copies synchronised.
Therefore, there is a need in the art to address the aforementioned problems.